The principal objective of this research is to understand the molecular mechanisms of mammalian DNA transcriptional control in normal cells and how alterations in such control may lead to malignancy. The major approaches are through 1) direct biochemical and biophysical analysis of defined, highly repetitive DNA sequences and their associated nucleoproteins by specific excision of the sequences from intact mammalian nuclei with restriction enzymes, 2) long-range DNA sequencing of the repeat units, 3) studies of DNA methylation patterns of the repeat sequences and 4) analysis of the nucleoproteins, including the histone and nonhistone proteins associated with the specific sequences. By focusing on simply organized and abundant DNA sequences in mammalian nuclei, unique opportunities are presented for understanding how specific nucleoproteins may interact with defined DNA sequences thereby regulate gene expression. Also, alterations in highly repetitive mammalian DNA sequences and DNA methylation have been strongly implicated in the processes of neoplastic transformation. The studies will be carried out in the context of present knowledge of chromatin subunit structure to expand that knowledge and to define the macromolecular configurations or chromatin packaging that may determine an important mode of transcriptional inactivation in the mammalian nucleus. Studies are also continuing on 1) the mode of action and properties of a class of seemingly site-specific mammalian endonucleases we have been isolating from mammalian testes, and their possible biological significance in alterations of the genome, and 2) the properties, sequence organization and distribution of highly conserved, highly repetitive DNA sequences that we have identified in all Old-World primates examined to date.